The invention is directed to improvements in fuel injection apparatus for an internal combustion engine. In a fuel injection apparatus of this kind, disclosed in U.S. Pat. No. 4,392,612, a pump piston axially guided in a cylinder bore of a pump housing is driven by a cam drive in a reciprocating manner. With its face end remote from the cam drive the pump piston defines a pump work chamber in the cylinder bore into which a fuel supply line discharges and which is connected via a pressure conduit to a protruding injection valve in the combustion chamber of the internal combustion engine to be fed. Thus, the quantity of fuel to be injected as well as the beginning of the high pressure delivery of the fuel found in the pump work chamber and therefore the beginning of the injection is regulated via the diversion process by means of a magnet valve disposed in the fuel feed line that opens on either end, which is triggered dependent upon the engine to be fed.
Since the fuel injection apparatus is highly sensitive to dirt particles due to an exact fit, the partially very small throughput cross sections, and the high working pressures, a fuel filter is inserted in the part of the fuel line of the known unit fuel injector that extends in the pump housing between the feed pump or the reservoir and the magnet valve. To that end, the pump housing was widened at the part which carries the magnet valve and a receiving chamber was provided for a filter insertion, which is held by means of the now relatively large screw neck of the fuel feed line.
The disposition of this fuel filter has, however, the disadvantage that it requires additional space in the unit fuel injector, which in modern internal combustion engines is not frequently available. Furthermore, the total weight of the unit fuel injector also is increased by means of the additional space, in addition to the manufacturing expenditure.